Conventionally, die bonding adhesives for forming a die bonding layer that is used to bond a semiconductor element to a support member for mounting the semiconductor element such as a lead frame have predominantly employed silver pastes. However, in the case of silver pastes, recent trends to larger semiconductor elements, together with reductions in the size of, and improvements in the performance of, semiconductor packages, have meant that the following problems have become more prevalent. Namely, these problems include paste protrusion following die bonding caused by the spreading properties of the paste, the occurrence of defects during wire bonding as a result of tilting of the semiconductor element, unsatisfactory precision in the thickness of the die bonding layer, and the occurrence of voids within the die bonding layer. As a result of these problems, satisfying the demands for further miniaturization and increased detail of support members in order to cope with these size reductions and performance improvements occurring within the semiconductor packages has proven difficult. Accordingly, in recent years, film-like adhesives that are advantageous for achieving further miniaturization and increased detail of support members have become widely used as die bonding adhesives (for example, see Japanese Patent Laid-Open No. H03-192178 and Japanese Patent Laid-Open No. H04-234472). These film-like adhesives are used, for example, in production methods for semiconductor packages (semiconductor devices) that employ individual bonding methods or wafer backside laminating methods.
In individual bonding methods, a film-like adhesive stored on a reel is cut into individual sections using a cutting or punching technique, and each of these individual sections is then bonded to a support member. Subsequently, a semiconductor element that has undergone singulation by dicing is die bonded to the support member via the film-like adhesive on the surface of the support member. Production of the semiconductor device is then completed by conducting a wire bonding step and a sealing step (for example, see Japanese Patent Laid-Open No. H09-17810). However, in the case of individual bonding methods, because a dedicated assembly device is required for cutting the film-like adhesive and bonding each individual section to a support member, the production costs are more expensive than systems that use silver paste.
On the other hand, in wafer backside laminating methods, the film-like adhesive is first laminated to the backside of a semiconductor wafer, and a dicing tape is then laminated to the bonded film-like adhesive. Subsequently, by conducting singulation by dicing the semiconductor wafer, semiconductor elements with an attached film-like adhesive are obtained, and each of these elements is then picked up and die bonded to a support member. Production of the semiconductor device is then completed by conducting a wire bonding step and a sealing step. In the case of this type of wafer backside laminating method, a dedicated assembly device for cutting the film-like adhesive and bonding each individual section to a support member is not required. This means that bonding can be conducted either by using a conventional silver paste assembly apparatus without modification, or by using a conventional apparatus that has undergone partial modifications such as the addition of a hotplate. As a result, this system is attracting considerable attention as an assembly method that uses a film-like adhesive and yet offers comparatively low production costs (for example, see Japanese Patent Laid-Open No. H04-196246).
However, recently, the quantity of so-called 3D package semiconductor devices, in which a plurality of semiconductor elements are stacked on top of a support member in order to increase the functionality of the device, has increased rapidly. Even with these 3D package semiconductor devices, because reductions in the thickness of the overall semiconductor device are still sought, further reductions in the thickness of semiconductor wafers continue to occur.
As semiconductor wafers become ever thinner, even in the production of semiconductor devices using the above type of wafer backside laminating methods, the occurrence of wafer breakage during transport of the semiconductor wafer or during the laminating of the film-like adhesive to the backside of the semiconductor wafer is becoming increasingly problematic. Accordingly, in order to prevent such wafer breakage, a technique in which a polyolefin-based protective tape (a backgrind tape) is laminated to the surface of the semiconductor wafer is now widely employed.
However, because the softening temperature of the backgrind tape is typically low (for example, no higher than 100° C.), in those cases where a backgrind tape is used, a film-like adhesive that is capable of being laminated to the semiconductor wafer backside at a temperature lower than the softening temperature (for example, 100° C.) is required. Furthermore, as semiconductor wafers become thinner, warping of the semiconductor wafer as a result of thermal stress becomes increasingly likely, and suppression of this warping also demands the use of a film-like adhesive that is capable of being laminated at as low a temperature as possible.
In this manner, the properties demanded of film-like adhesives include those properties that ensure favorable processability during the production of a semiconductor device, such as favorable bonding properties at low temperatures. In addition, in order to ensure favorable reliability for the semiconductor device, the film-like adhesive also requires satisfactory reflow resistance.
A film-like adhesive comprising a combination of a thermoplastic resin with a comparatively low glass transition temperature and a thermosetting resin has already been proposed as an adhesive that combines favorable processability and reflow resistance (for example, see Japanese Patent Publication No. 3,014,578).